Low temperature selective catalytic reduction of NO with NH3 over Mn-Fe spinel: Performance, mechanism and kinetic study

(Fe3-xMnx)(1-delta)O-4 was synthesized using a co-precipitation method and then developed as a catalyst for the low temperature selective catalytic reduction (SCR) of NO with NH3. The SCR activity of (Fe3-xMnx)(1-delta)O-4 was clearly enhanced with the increase of Mn content. The results of in situ DRIFTS study demonstrated that both the Eley-Rideal mechanism (i.e. reaction of activated ammonia with gaseous NO) and the Langmuir-Hinshelwood mechanism (i.e. reaction of adsorbed ammonia species with adsorbed NOx species) might happen during the SCR reaction over (Fe3-xMnx)(1-delta)O-4. According to the kinetic analysis, the respective contribution of the Langmuir-Hinshelwood mechanism and the Eley-Rideal mechanism on the SCR reaction was studied. Only the adsorption of NO + O-2 on (Fe2.8Mn0.2)(1-delta)O-4 was promoted, so the Langmuir-Hinshelwood mechanism predominated over NO conversion on (Fe2.8Mn0.2)(1-delta)O-4 especially at lower temperatures. Both the adsorption of NO + O-2 and the adsorption of NH3 on (Fe2.5Mn0.5)(1-delta)O-4 were obviously promoted, so NO conversion on (Fe2.5Mn0.5)(1-delta)O-4 mainly followed the Eley-Rideal mechanism especially at higher temperatures. Both the nitrate route and the over-oxidization of adsorbed ammonia species contributed to the formation of N2O on (Fe2.8Mn0.2)(1-delta)O-4 above 140 degrees C. However, the formation of N2O on (Fe2.5Mn0.5)(1-delta)O-4 mainly resulted from the over-oxidization of adsorbed ammonia species. Although the activity of (Fe2.5Mn0.5)(1-delta)O-4 was suppressed in the presence of H2O and SO2. the deactivated catalyst can be regenerated after the water washing. (C) 2011 Elsevier B.V. All rights reserved.